Glycols such as ethylene glycol and propylene glycol are valuable materials with a multitude of commercial applications, e.g. as heat transfer media, antifreeze, and precursors to polymers, such as PET. The market for ethylene and propylene glycols (EG and PG) is expanding worldwide, with the EG market being vastly bigger than the market for PG (i.e., 1,2-propylene glycol). Ethylene and propylene glycols are typically made on an industrial scale by hydrolysis of the corresponding alkylene oxides, which are the oxidation products of ethylene and propylene, produced from fossil fuels/petrochemical feed stocks involving multiple processing steps. Use of bio-based feed stocks for the production of energy and chemicals has become increasingly desirable in the industry since this approach to use feeds from renewable sources provides a pathway for sustainable development.
In recent years, increased efforts have focused on producing chemicals, including glycols, from renewable feedstocks, such as carbohydrate-containing feedstock. Carbohydrates are plentiful and renewable bio-mass feeds, and have the structural features resembling that of ethylene glycol; each carbon has one attached hydroxyl group or contains an oxygen function that can be readily converted into a hydroxyl. As such, EG and PG can be produced if the C—C bonds are selectively cleaved into C2 and C3 units.
As with many chemical processes, the reaction product stream in these processes comprises a number of desired materials as well as diluents, by-products and other undesirable materials. During the hydrogenolysis of glucose and glucose-containing molecules, to form EG and PG, some of the glucose is hydrogenated to sorbitol. Sorbitol cannot undergo retro-aldol conversion to form EG and PG in the hydrogenolysis reaction. As a result sorbitol is a side product and decreases the overall yield of the higher valued EG and PG. In order to provide a high value process, the desirable product or products must be obtainable from the reaction product stream in high purity with a high percentage recovery of each product and with as low as possible use of energy, chemical components and complex equipment.
Therefore, it would be advantageous to provide an improved method suitable for the production of glycols from the by-product, sorbitol, in order to make the overall glycol production process more economical than processes disclosed previously in the industry.